Many general comments are made in the patent and technical literature that the Friedel-Crafts type acylation of .beta.-substituted naphthalenes can be carried out in the presence of any Friedel-Crafts catalyst. This statement is then substantiated by particular reference to experiments using, e.g., aluminum chloride or zinc chloride catalyst in nitrobenzene or chlorinated hydrocarbons, or boron trifluoride optimally in the presence of hydrogen fluoride.
Typically these references do not identify the position of the acyl substitution on the naphthalene ring or do not provide such substitution in the 6-position with sufficient regioselectivity that a large scale manufacturing program can be developed using the disclosed technology.
In our work on developing precursors for aromatic monomers for polyesters, pharmaceuticals, and other value-added chemicals, we were interested in obtaining nearly exclusively 6-acyl-2-naphthol and related 6-acyl-2-substituted naphthalenes in high conversions with high regioselectivity.
A search of the literature provided the following pertinent prior art.
Japanese Kokai Sho No. 54 [1979]-135756, Yasui et al., describes the preparation of 2-alkyl-6-acylnaphthalene from the 2-alkylnaphthalene and acyl fluoride in hydrogen fluoride with boron trifluoride as a catalyst and in boron trifluoride as a catalyst-solvent. The reaction is claimed to be carried out at between -50.degree. C. and +100.degree. C.; however, a reading of the textual portion of the disclosure teaches that yields and 6,-2-selectivity decrease markedly outside the range of about -10.degree. to +10.degree. C.
Eiglmeier, in U.S. 4,082,807, teaches the acylation of 2-methoxynaphthalene in anhydrous hydrogen fluoride with diketene to yield 1-acetoacetyl-2-methoxynaphthalene in 88% yield at -25.degree. C. to -35.degree. C.
Additional literature which teaches the Friedel-Crafts acylation of naphthalene and its .beta.-substituted derivatives include:
Alvarez in U.S. Pat. No. 3,758,544, and U.S. Pat. No. 3,873,594, teaches that in conventional inert solvents, i.e., chlorinated hydrocarbons, Friedel-Crafts acylation of 2-methoxynaphthalene with acetyl chloride is accomplished in only low yields. He found that chlorination in the 1-position was necessary to improve the yield of the corresponding 6-acetyl derivative. In the cited patent, anhydrous hydrogen fluoride is identified as a typical but not preferred Friedel-Crafts catalyst.
Muessdoerffer and Niederprum in German Offenlegungschrift No. 2,616,986, published Oct. 27, 1977, claimed the acylation of phenols and substituted phenols with an acyl chloride in the presence of hydrogen fluoride to yield the 4-acyl derivative in high yield with high selectivity. The inventors disclose that 2-naphthol and 7-chloro-2-naphthol can be acylated according to their invention. They do not teach a method for the acylation of the naphthol derivatives nor do they indicate what isomer or isomers are manufactured by the claimed process. In view of the other cited prior art, one might be presumed to forecast that the 1-acyl-2-hydroxynaphthalene would be formed.
Lodewijk, U.S. Pat. No. 3,803,245, discloses the acylation of 2-methoxynaphthalene using aluminum chloride catalyst in nitrobenzene with aluminum chloride, zinc chloride, or similar Friedel-Crafts catalysts.
Organic Synthesis, Vol. 53, p.5, teaches the acylation of 2-methoxynaphthalene in nitrobenzene with acetyl chloride in 45-48% yield.
Further references teaching the acylation of naphthalene in Friedel-Crafts type reactions include:
______________________________________ Kacer and Krause U.S. Pat. No. 1,841,445 Kranzlein et al. U.S. Pat. No. 1,910,470 Skraup U.S. Pat. No. 1,995,402 Skraup U.S. Pat. No. 2,087,213 Boese U.S. Pat. No. 2,214,117 Lieber U.S. Pat. No. 2,287,110 Mikeska and Lieber U.S. Pat. No. 2,288,319 Lieber U.S. Pat. No. 2,307,891 Lieber U.S. Pat. No. 2,353,053 Johnson and Graber U.S. Pat. No. 2,683,738 Alvarez U.S. Pat. No. 3,637,767 Giordano and Casagrande U.S. Pat. No. 4,328,356 ______________________________________
Given and Hammick, Journal Chemical Society (1947) 1237
Bui-Hoi et al., Journal Organic Chem., 16,988-94 (1951)
Gupta and Haksar Agra Univ. J. of Res., (Sci) XI, Pt. 2, 165-6 (1962)
Arai, Tetrahedron Letters, 24, #14, pp. 1531-34(1983)
Girdler et al., Journal Chemical Society [1966] C(Org.), 181
Harrison et al., Journal Med. Chem., 13,203(1970) and the following Chemical Abstract references:
CA 50,5625 c PA1 CA 50,7139 e PA1 CA 56,14136 d PA1 CA 57,15022 d PA1 CA 58,6663 e PA1 CA 67,10907 y PA1 CA 74,16093 w PA1 CA 80,2790 h PA1 2-naphthol PA1 2-methylnaphthalene PA1 2-ethylnaphthalene PA1 2-isopropylnaphthalene PA1 2'-(sec-butyl)naphthalene PA1 2-methoxynaphthalene PA1 2-ethoxynaphthalene PA1 2-n-propoxynaphthalene PA1 2-(tert-butoxy)naphthalene PA1 2-methylthionaphthalene PA1 2-ethylthionaphthalene PA1 2-isopropylthionaphthalene PA1 2-fluoronaphthalene PA1 2-chloronaphthalene PA1 2-bromonaphthalene PA1 2-iodonaphthalene, and the like.
The process of this invention leads to intermediates in the manufacture of valuable pharmaceuticals as disclosed in the Alvarez patents, cited above. The process also provides intermediates for the manufacture of monomers as disclosed in the Yasui Japanes patent, loc cit.
Using the teaching of the above cited references, commercialization of the process has been difficult. Aluminum chloride, zinc chloride, and similar salts used as catalysts in their anhydrous state absorb water rapidly, hydrolyzing, and thus becoming useless in the reaction. Nitrobenzene and the polyhalogenated hydrocarbons utilized as solvents are high boiling, toxic materials.
Nitrohydrocarbons, in the presence of the water invariably required during the usual work-up, give rise to inseparable emulsions. Also, the usual Friedel-Crafts catalysts, when admixed with nitrohydrocarbons, generate a substantial exothermic reaction which can be difficult to control. Conversions are low. When using metal halides in nitrohydrocarbons, isomeric mixtures are common, causing additional separation steps to be necessary.
For all of the above reasons and others, we developed the herein claimed process.